Field of the Invention
The present invention relates to an image capturing apparatus, such as a digital still camera and a digital video camera, and to a control method for the same.
Description of the Related Art
Generally, an image capturing apparatus, such as a digital camera, detects a vibration of the image capturing apparatus itself and corrects image blur due to the vibration. More specifically, the image blur is corrected with an image blur correction apparatus driving a lens movable member (an image stabilizing lens and a holding member for the image stabilizing lens) that is movable in a manner so as to correct the image blur.
In many cases, the image blur correction apparatus uses an angular velocity meter and an accelerometer to detect the vibration. For example, various optical devices include an image stabilization apparatus that detects angular vibration with the angular velocity meter and moves a part of imaging lenses and an image sensor to reduce the image blur.
However, near distance imaging might involve a non-negligible amount of image deterioration due to what is known as parallel vibration. The parallel vibration acts in a horizontal or an orthogonal direction on a plane orthogonal to an optical axis of a camera and cannot be detected only with the angular velocity meter.
For example, when macro imaging with a distance of approximately 20 cm to an object is performed, the parallel vibration needs to be actively detected and correction for the vibration needs to be performed. The accelerometer is mainly used for detecting the parallel vibration.
The image blur correction apparatus obtains the amount and the direction of the vibration from acquired angular velocity information and acquired acceleration information, and outputs a correction position control signal for driving the lens movable member in a manner so as to cancel out the image blur. When the lens movable member is driven, a movable member position signal, indicating a current position of the lens movable member, is fed back to the image blur correction apparatus.
Then, the image blur correction apparatus outputs the correction position control signal corresponding to the movable member position signal, whereby feedback control is achieved.
Japanese Patent Application Laid-Open No. 2013-104921 proposes an image stabilization apparatus and an image capturing apparatus capable of achieving power saving by operating and stopping image blur correction in accordance with a focal length and an object distance (imaging magnification) while an object image is being displayed as a moving image on a liquid crystal display (LCD).
Digital cameras can display a moving image on a screen, such as an LCD. Even if there is an image blur which affects an object image to be recorded, such an image blur may not affect the object image displayed as a moving image. More specifically, the image blur may be unrecognized by a user.
In a case where the image blur correction is performed while the moving image is being displayed as described above, power is wastefully consumed for the image blur correction even for an image blur not affecting the moving image, in imaging performed on the wide angle side.
Thus, Japanese Patent Application Laid-Open No. 2013-104921 discusses the following control performed while a moving image, captured on the wide angle side having a small focal length, is being displayed. More specifically, whether the amount of displacement of the object image to be displayed, due to an image blur, exceeds a pixel pitch of the display screen is determined. In a case where the result indicates that the image blur of the object image to be displayed is unrecognizable or is relatively negligible by the user, an image blur correction mechanism is operated with a lower vibration suppression rate or is turned off.
When the image blur of the object image to be displayed is recognizable by the user, the image blur correction mechanism operates with a high vibration suppression rate. As described above, the angular vibration and the parallel vibration have a large effect on, for example, the macro imaging in which the object distance is small and the imaging magnification is large. Thus, the image blur correction mechanism operates with a high vibration suppression performance in accordance with the object distance even when image capturing is performed on the wide angle side.
Generally, in image data acquired by the image capturing apparatus, a marginal area including the four corners is likely to be darker than the center. Reduction of light amount in the marginal area relative to the center is known as shading. A larger reduction of the light amount in the marginal area (marginal illumination) relative to the center leads lower quality of image data.
The reduction in the marginal illumination is a characteristic derived from a lens that may be regarded as a cause of the difference in the brightness among the four corners. The reduction in the marginal illumination fluctuates in accordance with a zoom magnification, that is, a zoom lens position.
Further, when an image stabilization lens shifts from the optical axis, the marginal illumination is reduced at an area opposite to the direction of the movement. The marginal illumination is also reduced by an error in the attached position of the image sensor.
All these causes of the reduction in the marginal illumination have been required to be taken into consideration for determining the range of movement of the correcting lens to obtain an image, to be displayed or stored, unaffected by the shading.
The marginal illumination might also be reduced by a position of a focus lens for a focus adjustment, depending on a configuration of an optical lens group. For example, this might be the case where the configuration of the focus lens group employs an inner focus system. More specifically, the marginal illumination might be reduced by the reduction in the effective focal length due to the movement of the focus lens towards the front lens side for focusing of when the macro imaging in which the object distance is near distance is performed.
Thus, as discussed in Japanese Patent Application Laid-Open No. 2013-104921, the reduction in the marginal illumination involved in the macro imaging might be obvious depending on the configuration of the optical lens group, in a case where the range of movement of the correcting lens is determined for each zoom lens position.
When the range of movement of the correcting lens is fixed to that for the macro imaging, there is a problem in that the range of movement is too small to obtain a sufficient correction effect for a large vibration occurring during normal imaging, such as image capturing while walking.
The present invention is made in view of the problems described above, and is directed to providing an image stabilization effect while image quality is prevented from largely deteriorating due to shading.